Think Create | Deqing Sun

Whistle Key Finder

by on Apr.30, 2010, under My gadgets

Keys are essential in our lives, but they may not be present when we need them. In this design, the circuit will respond to the whistle’s sound and make theirs. Then the keys can be founded easier with our ears.

The first design used band pass filter to do the work. It works well, but it suffers a lot to adjust the resistors values because it depends on those values to determine the various parameters of the filter. So it can hardly be built on a small piece of board to reduce its size.

The second design uses a different principle. It uses a Phase Lock Loop to catch the tone of a whistle. The PLL can catch a certain frequency in the background noise. And only the parameters of the VCO are essential. So a single potentiometer to adjust the oscillating frequency will do and other components have a high tolerance of inaccuracy.

The circuit has two stages. The first one uses an op-amp to amplify the signal from the microphone. This will greatly increase the sensitivity of the circuit. Then the signal can be coupled to the tone decoder to detect the whistles frequency. When it is detected, the output pin will sink in current.

In order to be informed when we need the gadget, a sound IC is attached to the circuit. One problem is that the trigger of the sound IC needs a rising edge. So a PNP transistor is used to invert the logic output and the gadget will “BARK!” when it hears the whistle.

Front Side:

Back Side:

So I can enjoy the NOISE when I want to find it.

9 Comments for this entry

  • IndarKness

    You can make a harmonica key recorder. When someone plays the harmonica, you can record the tunes and notes.

  • seer

    But I have to take the Digital Signal Process course first to analyze the frequency spectrum.

  • IndarKness

    You recorded the whistle and found its frequency, right. If you have time you can do it exactly as same as this whistle key finder.

  • raihan

    what type of tone decoder that use in this circuit??LMC567CM/NOPB @LMC567CN ???

  • seer

    I used a LMC567CN. The difference is only in the package.

  • spulka

    But how long will the battery last? You need to power the microfone, the op-amp and the decoder all the time.

  • seer

    The microphone is only a sound controlled mosfet. Both the op-amp and the decoder are based on CMOS tech and able to work at 2V. So the whole circuit consumes less than a single micro-amp. So it can last for several months.

  • maita

    If I whistle with my mouth will it be able to activate?

    And where would I find all the circuitry.

    I am not a novice but, I would like to try to build this my self.

    Thank you.

  • seer

    It highly depends on frequency of your whistle. I guess you can do that with some practice. You can get all components from digikey or any distributor like that.

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